When screw pumps, such as twin, rotary screw pumps, are employed for the pumping of high density fluids, such as aqueous suspensions of thick fibrous matter like high density paper pulp stock, Athabasca froth (which contains sand), and the like, the clearance between screws and pump bodies is affected by the fluid pumped. Substantial radial forces are generated which cause shaft deflection. This condition causes wear and leakage.
Severe wear can be experienced in the stuffing boxes of prior art screw pumps because of the excessive shaft deflection that takes place through this area, particularly in pumping high density fluids. Not only does the packing severely score the shaft sleeve, but also the throat bushing badly galls the shaft sleeve, creating a condition wherein excessive fluid being pumped leaks out of the stuffing box making the surrounding area where the pump is located very wet and dirty.
For example, in one twin rotary screw pump type, the initial clearance between the screws and the pump body is about 0.020 inch radially. Because of the radial forces generated in service when pumping high density paper pulp stock, the screws operate with a zero side clearance on one side, and, when new, with a clearance on the opposite side of about 0.040 inch. As wear occurs, this spacing increases. Since the pump is assembled with all parts concentric about the body core center line, in service the shaft becomes eccentric in the stuffing box bore to approximately 0.010 inch.
The state of the art is represented by my prior U.S. Pat. Nos. 2,994,562 and 3,841,805. There is a need in the art for means which will extend the pump duty life because of the wear and leakage problems above indicated.